There is known a compound having a structure that a shaft 1 passes through a ring 2 and end caps 3 are bonded to both ends of the shaft 1 so as to prevent the escaping of the ring 2 as shown in FIG. 1. This compound is called as a rotaxane. Here, it is expressed that the shaft 1 and the ring 2 are connected through mechanical bonding. Since the ring 2 can freely conduct the rotation or translation motion on the shaft 1, it is studied to apply the compound to a molecular switch or the like, for example, by controlling the position of the ring 2 through external stimulation.
As a synthesis of the rotaxane is known a slip method wherein rotaxane bond is produced by thermal pushing with a complementarity of size between the shaft and the ring. Also, there is known a method wherein a pseudorotaxane 4 is produced by a host-guest interaction between the shaft 1 and the ring 2 and thereafter the end caps 3 are bonded to both ends of the shaft 1 as shown in FIG. 2. In the latter method, the yield of the rotaxane is controlled by a complexing ratio of the shaft 1 and the ring 2 in the pseudorotaxane 4 and a kinetically process in the bonding reaction of the pseudorotaxane 4 and the end cap 3.
On the contrary, the inventors have developed a synthesis method of the rotaxane based on kinetic control utilizing an equilibrium reaction being a thiol-disulfide exchange reaction. In this synthesis method, a bifunctional ammonium salt having a disulfide bond is used as the shaft 1 and thiols are added thereto, whereby the disulfide bond is reversibly cleaved through the exchange reaction with the thiols as shown in FIG. 3. In the cleavage of the shaft 1, the ring 2 such as crown ether or the like forms a complex with the ammonium salt to produce [2]rotaxane 5 or [3]rotaxane 6. In the above synthesis method, since all reaction process is the equilibrium reaction, the production of the rotaxane is kinetically controlled and hence the product yield is dependent upon the relative stability, so that [2]rotaxane or [3]rotaxane can be selectively synthesized in a high yield.
On the other hand, there are studied high polymers having plural rotaxane structures in their molecules as shown in FIG. 4 or so-called polyrotaxanes and also the application to new materials or functional materials are studied. In FIG. 4, (A) is a polyrotaxane having a structure that the shaft 1 is a main chain polymer having end caps 3 at its both ends and plural rings 2 pass through the shaft 1, and (B) is a polyrotaxane having a structure that the shaft 1 is a chain molecule having end caps 3 and the ring 2 is a polymer obtained by connecting a plurality of rings 2 through covalent bonding and the shafts 1 are passed through the respective rings 2, and (C) is a polyrotaxane having a structure that a plurality of shafts 1 each having an end cap 3 in its one end are bonded to a main chain polymer and each of the shafts 1 passes through the ring 2. With respect to crosslinked bodies by crosslinking polymers with the rotaxane structure, however, there are not yet conducted sufficient examinations.
Now, there are known a polyurethane consisting of a polyfunctional polyol and diisocyanate and a polyurethane consisting of a bivalent polyol, diisocyanate and diamine. The former is excellent in characteristics owing to the crosslinking through chemical bond, but is difficult in the decrosslinking and hence is difficult in the recycle, while the latter is easy in the decrosslinking owing to the crosslinking through hydrogen bond but is poor in the characteristics. That is, the conventional crosslinked bodies do not simultaneously possess the excellent characteristics and the easiness of the decrosslinking (see Sinzou Yamashita, Kouei Komatsu et al. Elastomer, Kyouritsu Shuppan, Feb. 20, 1989, pp. 61–77).